awakens default getter synthesis from the untyper nightmare

Our happy little macro paradise is regularly invaded by resetAllAttrs,
the bane of all macros and typers. It’s so ruthless and devastating that
we’ve been long scheming to hack something really cool and to one day
defeat it.

Today we make the first step towards the happy future. Today we overthrow
the UnTyper, resetAllAttrs’s elder brother that rules in the kingdoms of
GetterLand and CaseClassia, and banish him from the land of getters.
In the name of what’s good and meta, let’s band together and completely
drive him away in a subsequent pull request!

To put it in a nutshell, instead of using untyper on a DefDef to do
default getter synthesis, the commit duplicates the DefDef and does
resetLocalAttrs on it.

As default getter synthesis proceeds with figuring out type and value
parameters for the getter, then its tpt and finally its rhs, the commit
destructures the duplicated DefDef and then assembles the default getter
from the destructured parts instead of doing copyUntyped/copyUntypedInvariant
on the original DefDef.

I would say the test coverage is pretty good, as I had to figure out
3 or 4 test failures before I got to the stage when everything worked.
Iirc it tests pretty exotic stuff like polymorphic default parameters
in both second and third parameter lists, so it looks like we're pretty
good in this department.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/reflect/scala/reflect/internal/Symbols.scala b/src/reflect/scala/reflect/internal/Symbols.scala
index 0dfcf06874..e15b33e5d7 100644
--- a/src/reflect/scala/reflect/internal/Symbols.scala
+++ b/src/reflect/scala/reflect/internal/Symbols.scala
@@ -801,9 +801,14 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
       isConstructor && !isPrimaryConstructor
 
     /** Is this symbol a synthetic apply or unapply method in a companion object of a case class? */
+    // xeno-by: why this obscure use of the CASE flag? why not simply compare name with nme.apply and nme.unapply?
     final def isCaseApplyOrUnapply =
       isMethod && isCase && isSynthetic
 
+    /** Is this symbol a synthetic copy method in a case class? */
+    final def isCaseCopy =
+      isMethod && owner.isCase && isSynthetic && name == nme.copy
+
     /** Is this symbol a trait which needs an implementation class? */
     final def needsImplClass = (
          isTrait